Disposal of hazardous waste is a pressing environmental problem. Hazardous waste such as radioactive materials from nuclear reactors have long term radioactivity which makes conventional methods of solid waste disposal inappropriate. There is significant danger of such materials leaching from a solid waste disposal facility and entering the water supply.
Vitrification of hazardous solid wastes has been proposed and implemented on a relatively small scale. Problems associated with vitrification processes developed previously include low throughput resulting in a high disposal cost per unit of hazardous waste material. As used herein, radioactive wastes, hazardous wastes and toxic chemical waste shall be referred to as “hazardous waste”.
The United States Department of Energy, working in conjunction with six other countries in a cooperative technical exchange, has developed a method of vitrifying radioactive waste material in boro-silicate glass. The U.S. Department of Energy project resulted in the development of an electric glass furnace. The glass furnace developed was electrically powered and operated on an aqueous waste stream having 40 percent solids content. The solids in the waste stream were approximately 60 percent boro-silicate glass frit and 40 percent radioactive waste sludge. A primary problem with the resultant static glass furnace was that its output was limited to a rate of 4 pounds of vitrified waste per hour per square foot of furnace surface area.
Boro-silicate glass was selected for its chemical durability and low melting point. The special boro-silicate glass combines with the waste material to form a vitrified output that will be referred to herein as “waste glass”.
The furnace included the use of Inconel 690 as electrodes and other parts of the furnace. (Inconel is a trademark of International Nickel Corporation).
In addition to the low throughput of the electric furnace, the cost of melters developed in the cooperative project was considerable. In addition, start-up and shut-down procedures require considerable time.
Soda lime glass melters having a mixing element and electrical heating have been developed for the purpose of improving productivity of soda lime glass manufacturing processes. An example of such a melter is disclosed in U.S. Pat. No. 3,850,606 to Rough and U.S. Pat. No. 3,819,350 to Pellett, et al.
Such melters were tried by Owens-Illinois but were abandoned due to the inability of the melters to produce high quality glass having an acceptable level of gaseous occlusions. The intended electrical flow path in the melters was between the electrodes extending upwardly from the floor of the melter and the mixing element. This general arrangement resulted in problems including high electrical charge concentration at the tips of the impeller which resulted in excessive wear and consumption of the impeller. Further, high volume waste processing is adversely effected by the use of components which must be replaced.
These and other problems are overcome by the glass vitrification melter of the present invention as summarized below.